A new plastic membrane for methanol fuel cells

How alternative plastic electrolytic membranes can help bring down the cost of fuel cells

Fuel cells may be an environmentally-friendly means of generating electrical energy, but they are also very expensive. Much of the cost of fuel cells is in the electrolytic membrane that separates the anode and cathode sites. To lower the cost, engineers are looking to replace traditional cell membranes with alternative materials.

A ceramic membrane containing iron oxide nanoparticles could provide an alternative to the traditionally used Nafion copolymer discovered in the 1960s by scientists at DuPont. But ceramics are by their very nature brittle, and it will be a challenge to use such materials in applications where catastrophic failure would render the devices instantly useless.

Engineers Avni Argun, Nathan Ashcraft and Paula Hammond at the Massachusetts Institute of Technology (MIT) in Cambridge, US, have created a membrane material in thin film form that can improve the power output of direct methanol fuel cells (DMFCs). “Our goal is to replace traditional fuel-cell membranes with these cost-effective, highly tuneable and better-performing materials,” says Hammond.

Current DMFCs are compromised by the fact that Nafion is permeable to methanol. This wastes fuel and lowers the efficiency of the cell.

Using layer-by-layer assembly the MIT team led by Hammond created a film based on a highly sulphonated form of poly(2,6-dimethyl 1,4-phenylene oxide), or sPPO for short. The film, which has the consistency of plastic wrap, is reported to be two orders of magnitude less permeable to methanol than Nafion, but compares favourably in terms of proton conductivity. In tests, the engineers coated a Nafion membrane with the new film and incorporated this into a DMFC. The result was an increase in power output of more than 50%.

So far the researchers have used the new film as a complement to Nafion. But at the same time they are exploring whether the film could be used on its own. “In the short run we are looking at modification of the current Nafion membrane to quickly implement our novel materials for commercialisation,” says Argun, who is lead author of the study published recently in Advanced Materials.

“The key thing we are working to improve is the processing time it takes to make these membranes,” says Argun. “Using a technique developed in our lab, we can reduce the fabrication time by over a factor of 25. This work is currently underway.” The equipment used in the study is designed for laboratory-scale work, but Argun notes that Avery Dennison is developing a commercial technology that can adapt the layer-by-layer assembly technique to a fast roll-to-roll process.

As well as fuel cells, the MIT film has potential for use in photovoltaic cells. “We are looking at using these materials as a solid-state electrolyte in dye-sensitised cells,” says Argun. “This is similar to previous work in our group, but our current layer-by-layer systems have superior ion transport properties and mechanical stability and integrity.”

The Hammond group’s fuel cell membrane work was funded through the DuPont-MIT Alliance, which expired at the end of 2007. It is now being supported by the National Science foundation. The researchers are open to interactions with other companies with a view to creating new partnerships.